Research shows that men whose mothers ate a lot of beef during pregnancy have lower than normal sperm counts and are also at risk for fertility problems.

Big Mac-munching expectant mothers beware: Recent research may prompt you to think twice about that hamburger craving.

Shanna H. Swan and a team of researchers from the University of Rochester Medical Center discovered that men whose mothers ate a lot of beef during pregnancy have lower than normal sperm counts and are also at a significantly greater risk for fertility problems.

"They found that, in general, the more beef a woman ate, the lower her son’s sperm count. For women who ate beef at least seven times a week, the son’s sperm count averaged 24.3 percent below normal. And even though those sons produced a pregnancy, they were three times as likely to have consulted a fertility doctor."

Swan suspects that low sperm counts are related to steroids given to U.S. cattle to make them meatier, or they might result from the animals’ exposure to pesticides and other environmental pollutants. Currently, many U.S. farmers give six growth hormones to cattle; Europe, on the other hand, banned these hormones in 1988, perhaps with good reason. Previous studies on rodents showed that even trace amounts of estrogen hormones in the uterus from food can lower an offspring’s sperm count. But prior to Dr. Swan’s research, published this week in the journal Human Reproduction, no one tested this effect in humans (a shocking fact that begs the question “Uhhh, why not?”).

Sons aren’t the only ones who may be suffering from beef-induced health problems, either.

"If the sperm deficit is related to the hormones in beef, Swan’s findings may be “just the tip of the iceberg,” wrote biologist Frederick vom Saal of the University of Missouri-Columbia in an editorial accompanying the paper.

In daughters of the beef-eaters, those same hormones could alter the incidence of polycystic ovarian syndrome, the age of puberty and the postnatal growth rate, he said."

The jury’s still out on whether beef is a no-no for expecting moms, but other typical pregnancy cravings are OK as far as we know. So go ahead, have another scoop of vanilla ice cream with pickle juice.

Story by Sarah Parsons. This article originally appeared in Plenty in March 2007. This story was added to MNN.com in July 2009.